In 2002 we were funded by the NASA Institute for Advanced Concepts to perform preliminary work on an antimatter-based propulsion system. This campaign seeks to fund a continuation of our mission to develop an antimatter thruster capable of reaching (or exceeding) 5% of the speed of light. The goal is to enable interstellar travel with the initial requirements of accelerating, decelerating, and studying a nearby solar system all within a human lifetime.
For a more complete presentation and a detailed look at our past work, go to http://www.antimatterdrive.org and view our ever-growing body of content.
When a person in the general public first finds out about the serious development of antimatter propulsion, their initial reaction is often "Can we make antimatter?" Our standard response is that humanity has already been able to produce 2 nanograms per year at the Fermi National Accelerator Laboratory ("Fermilab"). In fact, one of our lead scientists worked at Fermilab for 14 years on antimatter production, storage, and usage. In fact, that scientist led, along with Bill Foster (now U.S. Congressman IL-11) [http://www.billfoster.com/], the approval, design and construction of the antiproton Recycler ring pictured below.
Can Enough Antimatter be Made?
By rotating the assembly the radiation damage could be spread out. By translating the assembly perpendicular to the beam direction, the depth of material seen by the protons and antiprotons could be varied in order to optimize antiproton production.
Antiprotons sometimes form for when a proton disintegrates upon collision with a target nucleus. The resultant particle shower sometimes includes an antiproton. For every million protons on target, Fermilab was able to capture 15 antiprotons. The thicker the target, the more protons can be converted into antiprotons. But as the target depth is increased, the newly created antiprotons are increasingly annihilated before exiting the target and scattered into a very diffuse cloud. In order to capture as many antiprotons as possible, a lithium lens was placed immediately behind the target to focus that cloud. One of the Fermilab lenses is pictured below.
After travelling through the lithium lens the antiprotons were directed into a pair of particle accelerators called the Debuncher and the Accumulator. The purpose of the Debuncher was to reduce the large energy spread of the antiprotons. The purpose of the Accumulator was to "stack" antiprotons into a tight beam. An important technology employed was stochastic cooling, the invention of which earned the Nobel Prize for accelerator physicist Simon van der Meer in 1984. These accelerators are shown in the picture below.
This state-of-the-art antiproton production infrastructure was designed to produce antiproton beams used in the Tevatron proton-antiproton collider in order to perform high-energy particle physics experiments, such as the discovery of the Top quark. For the purpose of fueling an interstellar mission, an optimized antiproton production infrastructure will be quite different.
First, instead of a thick target, a very thin target will be used. While this geometry will produce fewer antiprotons per accelerated proton, the antiprotons that come off the target will form a much tighter beam. The anticipated yield of antiprotons per proton is expected to be close to 1%. By utilizing multiple targets the same number of proton interactions can be generated. Therefore, the increase in antiproton intensity is expected to be near a factor of 1000.
Second, the number of protons can be increased. A relatively modest proton intensity increase factor of 5 is assumed.
Third, instead of the use of synchrotrons such as the Main Injector, linear acceleration for the same proton beam current yields an increase antiproton production factor of 200,000. Applying all of these improvement factors, the antiproton production rate can be increased from 2 nanagrams per year to 2 grams/year. An antiproton production rate of 2 grams/year is sufficient to fuel an interstellar mission every decade or so. During the course of the research supported by this campaign further upgrades will be invoked to decrease the mission fueling time toward the goal of less than 4 years.
How Much Would it Cost?
Choice of Antimatter Fuel
But at 5% of the speed of light, it would take 90 years to reach the nearest confirmed planet Proxima b. We have concluded that travelling through a solar system at this velocity would preclude any measurements that would yield useful information. Therefore, the spacecraft would need to decelerate and go into orbit around either the star or Proxima b itself. To decelerate from this velocity, antimatter would need to be transported across the interstellar void.
The storage of antihydrogen for this period of time would be quite problematic. Like its normal matter cousin, antihydrogen has a high vapor pressure even at cryogenic temperatures. This means that antihydrogen molecules would continuously boil off the surface of the solid antihydrogen snowflakes that were originally envisioned. We need a fuel with a much lower vapor pressure.
So the answer comes down to producing nuclei containing antineutrons. After considerable study of the literature, the proposed first step in the process of nucleosynthesis is the reaction in which two 70 MeV antiprotons are collided to produce an antideuteron (an antiproton bonded to an antineutron) plus a negative pi-meson. In actuality the two antiprotons would not be at the same energy so as to produce the antideuteron with a kinetic energy high enough to be efficiently captured by a third storage ring.
As seen in the sketch below, half of these stored antideuterons are then collided with antiprotons to form antihelium-3 (one antiproton plus two antineutrons). The other half of the antideuterons are collided with half of the antihelium-3 nuclei to from antihelium-4 (two antiprotons bonded to two antineutrons). This reaction also produces an antiproton that is trapped and used over again. The last stage is to collide the antihelium-3 and the antihelium-4 nuclei to from antiberyllium-7.
There are a couple of points to note in this nucleosynthesis plan. First, all of these reactions are well measured with their normal matter cousins. Second, collision energies and partners were chosen so that theoretically no antimatter is lost in the entire process. The loss is restricted to mass-less gamma-rays and low-mass pi-mesons.
Once the antiberyllium-7 is produced it is decelerated and stored in an electromagentic trap. By itself, the antiberyllium-7 nuclei are stable. But the next step is the introduction of positrons to form atomic antiberyllium-7. By cooling the antiberyllium-7 nuclei into a crystal lattice wherein their mutual repulsion creates coupling between the nuclei, this positron capture will be enhanced.
Once converted into atomic antiberyllium-7, positron capture decay will occur with a 53.22 day half-life. Eventually all of the antiberyllium-7 decays into antilithium-7, which is stable.
The long-term storage and manipulation of grams of antillithium will be addressed in a future campaign. The current campaign will concentrate on designing the specific particle accelerator hardware and detailing the production rates at each step of the above process. Cost estimates of the equipment and operations will be generated. Basically, we will produce a design report that can be used to build an antilithium factory. This design report will also be used as the basis for future experiments (funded by future campaigns) wherein this entire nucleosynthesis plan will be tested using normal matter (to keep expenses down).
Use of Funds
- Design the particle accelerator complex needed to produce several grams of antiprotons each year.
- Estimate the equipment and operational costs of such a complex.
- Produce a design report that specifies all of the processes and equipment necessary for the production of antilithium, the proposed antimatter fuel of choice for interstellar missions requiring deceleration once at the destination solar system.
- Estimate the equipment and operational costs for antilithium production.
- Plan a program of future campaigns aimed at experimentally demonstrating the nucleosynthesis and storage of antilithium (using normal matter to keep costs low).
Risks and challenges
The goals of this campaign are purposely restricted to tasks that do not require permission or cooperation from external entities such as NASA or Fermi National Accelerator Laboratory. Instead, we will concentrate on designs and reports aimed at bolstering future campaigns, giving us the necessary time to reestablish such relationships.
Because we are new to crowdfunding, we have promised only one reward that requires shipping and handling. All other deliverables will be electronic in nature, allowing us to concentrate our efforts on the science. If there is a significant demand for items such as T-shirts, mugs, or other tangible items, we will consider expanding our rewards categories appropriately in the future.Learn about accountability on Kickstarter
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